1. Field of the Invention
The present invention generally relates to a method for identifying a wafer serial number. In particular, the present invention is directed to a method for identifying a wafer serial number by means of accumulating multiple and independent digit results.
2. Description of the Prior Art
In the semiconductor manufacturing process, a wafer always undergoes many procedures, such as lithography, exposure, etching, ion implantation, cleaning, etc. In order to increase the efficiency and the yield, there are multiple wafers together undergoing the same procedure in each single procedure. In order to distinguish each wafer which undergoes the same procedure at the same time, every wafer has a unique number. This unique number is called a “wafer serial number.”
A wafer serial number usually includes a plurality of digits. Each digit may be any one of a character such as A, b, Γ or δ, a number from 0-9 or a symbol such as #, % or £. Under the combination of characters, numbers and symbols, every wafer is capable of having a unique number. In order to distinguish each wafer, a step called “wafer serial number identification” is needed. The step, namely the wafer serial number identification step, is usually accomplished by optically reading every digit of the wafer serial number so as to obtain all of the digit results of the wafer serial number of this wafer. However, in the current method for identifying a wafer serial number, a plurality of specific identification recipes are used to identify the digit results of each and every one of the digits in a wafer serial number. Supposing a certain identification recipe may identify all of the digit results of each and every one of the digits in a wafer serial number, a complete wafer serial number can accordingly be obtained.
However, in a practical operation, the outcome is not always so straightforward and simple as expected. Every possible reason, such as scratches or stains, may substantially jeopardize the read rate of any digit in the wafer serial number. If under a certain condition, i.e. an identification recipe, all digit results of the digits in the wafer serial number of a wafer cannot be completely identified, in other words any one of the digits fails to be successfully read under a certain condition during an identification procedure, the identification condition is determined to fail to read and no complete wafer serial number is successfully obtained.
Nevertheless a complete wafer serial number is still required, so another identification condition is used to identify all digit results of the digits in the wafer serial number of a wafer. If under such new identification condition all digit results of the digits in the wafer serial number of a wafer can be identified, a complete wafer serial number is therefore obtained. However, if under such new identification condition not all digit results of the digits in the wafer serial number of a wafer can be identified, that is, any one of the digits fails to be read under this condition, it is still considered a reading failure so still no complete wafer serial number is successfully obtained. At this time, still another identification condition is used to identify all digit results of the digits in the wafer serial number of a wafer till all the digit results of the digits in the wafer serial number of a wafer are successfully identified to obtain a complete wafer serial number.
But, when all of the identification conditions are not able to identify all the digit results of the digits in the wafer serial number, by any means there is no complete wafer serial number can be obtained at all. This is a serious problem because the wafer serial number is abnormally processed and the unknown wafers cannot be distinguished, even worse the manufacturing process and the yield are severely compromised.
As a result, a novel method to identify a wafer serial number is still needed. Such novel method should decrease the possibility of abnormal reading rate of the wafer serial number without substantially changing the current process.